Under certain conditions current() can fail.

- Added spaces preset default handling.
- Cleaned up spaces contextual link generation and added a hook to allow other modules to modify contextual links.
- General cleanup and logic reworking for multiple space implementations.

- Added hook_views_tables() for implementing an abstract space filter.
- Added integration against the views space filter in spaces_og,
spaces_core, spaces_calendar and spaces_casetracker.
- Removed old og views handler cruft.

- Adding stricter check before iterating locked features.

- Removing spaces.theme include and merging single theme function into spaces.module

- Removed spaces date constants.